Various types of customizable integrated circuits are known in the art. The following U.S. patents are believed to represent the state of the art: U.S. Pat. Nos. 5,903,490; 5,742,181; 5,679,967; 5,260,597; 5,049,969; 4,933,738; 4,960,729; 4,924,287; 4,240,094. Reference is also made to UK Patent 1135992 and to the various references appearing in the foregoing patents.